How To Install Spark Plugs in Vehicles

by Contributing WriterUpdated June 12, 2017

The spark plug is one of the most important components in the Vehicles engine. It controls the flow of electricity from the distributor cap and sends a charge into the cylinder. The spark then ignites the fuel, driving the piston back down Vehicles the next revolution. The combustion process in the gas engine cannot complete itself without the spark. If there is a noticeable decline in your engine performance or it seems you are using more gas than normal, it is probably time to change the plugs.

Install a memory saver according to the memory saver’s instructions. Remove the negative battery cable from the battery, using a combination wrench.

Lift the front of the LS with a floor jack and slide jack stands under its frame rails. Lower the vehicle onto the frame rails.

Allow the vehicle to sit until the engine is cool to the touch. Unscrew the cap from the radiator degas bottle. Position a drain pan under the radiator petcock and turn the petcock counterclockwise to start the flow of coolant. Close the petcock once the flow of coolant stops.

Raise the LS, remove the jack stands and lower the car to the ground.

Pull the crankcase ventilation tube and fuel vapor tube from the air filter outlet tube and set them aside. Loosen the two air filter outlet tube's hose clamps with a ratchet and socket, and remove the tube from the engine compartment.

Lift each wiper blade off the windshield and place a strip of masking tape under the wipers. Lower the wipers to the masking tape, then trace along each wiper blade with a pen, leaving an alignment mark on the masking tape.

Pry the wiper arm-retaining nut covers from each wiper arm, using a flat-head screwdriver. Remove the wiper arms’ retaining nuts, using a ratchet and socket. Pull the wiper arms from the vehicle.

Remove the six pin-style retaining clips from the windshield cowl by prying them off with a flat-head screwdriver. Lift upward on the cowl to release its retaining clips and remove it from the vehicle.

Unfasten the seven bolts securing the engine crossover brace to the vehicle, using a ratchet and socket, then pull the brace from the vehicle.

Unplug the throttle position sensor and electronic throttle control -- the two electrical components on the throttle body – wiring harnesses from their receptacles.

Pull the brake booster vacuum hose – the large vacuum hose directly behind the throttle body – from its inlet on the intake manifold. Pull the evaporative emissions hose – the hose behind where the brake booster hose was – from the intake manifold. Pull the PCV tube from the front, passenger’s side of the intake manifold, then from the PCV valve, which is on the driver’s side valve cover.

Find the two coolant hoses on the front passenger’s side of the intake manifold. Slide the hose clamps 3 inches down the hoses, using slip-joint pliers, then pull the hoses from the manifold with a slight twisting motion.

Pry the PCV tube and coolant hose routing clip from the intake manifold, using a flat-head screwdriver. Position the PCV tube and coolant hose, which several plastic retainers hold together, aside and out of the way of the intake manifold.

Remove the front manifold bracket-to-intake manifold bolt, which is on the front passenger’s side of the intake manifold, using a ratchet and socket.

Unplug the two intake manifold tuning valve connectors from the IMT valves on the rear passenger’s side of the intake manifold. Disconnect the fuel pressure sensor wiring harness, which is on the rear driver’s side of the upper intake manifold. Pull the fuel pressure sensor vacuum hose -- the hose next to the pressure sensor’s wiring harness -- from the intake manifold.

Unfasten the passenger’s side manifold support brace-to-intake manifold bolt, which is on the lower passenger’s side of the intake manifold, using a ratchet and socket. Remove the four upper intake manifold-to-lower intake manifold bolts. Lift the upper intake manifold from the lower intake manifold and remove it from the engine compartment.

Pull the upper intake manifold gasket from the engine and put a clean shop cloth over the inlets into the lower intake manifold to prevent debris from getting into the engine. With the intake manifold removed, you have a clear view of all six coil packs.

Spark Plug Replacement

Check the gap on all six new Motorcraft AGSF-32FS spark plugs using a spark plug gap tool. The 3.0-liter engine requires a gap from 0.051 to 0.057 inches. Exchange any incorrectly gapped plugs for new ones, as these plugs are not adjustable.

Unplug the wiring harnesses from all six ignition coils. Remove the bolt securing each ignition coil to the engine, using a ratchet and socket, then pull each ignition coil from the engine with a slight twisting motion, exposing the six spark plugs.

Remove all six spark plugs with a ratchet, 6-inch extension and spark plug socket.

Hand-thread the replacement plugs into the engine using the 6-inch extension and spark plug socket. Tighten the spark plugs to 11 foot-pounds with a torque wrench.

Apply a dab of dielectric grease inside the boot on the base of each coil pack and spread the grease around the inside of the boot with a small flat-head screwdriver. Guide the coil packs into the spark plug tubes and press them downward until each one clicks on its respective spark plug – you can install any coil pack on any plug. Tighten the coil packs’ retaining bolts to 44 inch-pounds with an inch-pound torque wrench and socket.

Plug the wiring harnesses into their respective coil packs. Each wire routes only to one coil pack to prevent incorrect connection.

Upper Intake Manifold Installation

Set a new upper intake manifold gasket into place and set the upper intake manifold onto the lower intake manifold. Hand-thread the upper intake manifold-to-lower intake manifold bolts.

Number the upper intake manifold-to-lower intake manifold bolts, starting from the front-most bolt and working counterclockwise around the intake manifold, 1 through 6.Tighten the bolts to 89 inch-pounds in the following order: No. 3, No. 4, No. 1, No. 6, No. 2, No. 5.

Install the passenger’s side manifold support brace-to-intake manifold bolt and tighten it to 89 inch-pounds. Plug the three wiring harnesses – two IMT valve and fuel pressure sensors – to the rear of the intake manifold. Plug the fuel pressure sensor vacuum hose to its inlet on the rear of the intake manifold.

Thread the front manifold bracket-to-intake manifold bolt by hand and tighten it to 89 inch-pounds. Route the PCV tube and coolant hose in the direction they were before you positioned them aside. Plug the PCV tube into the PCV valve on the driver’s side valve cover. Press the PCV tube and coolant hose retaining bracket into its recess in the intake manifold.

Plug the two coolant hoses into their respective inlets on the upper intake manifold and slide the hose clamps to within 1/2-inch of each hose’s end. Press the evaporative emissions hose and PCV tube into their respective inlets on the intake manifold. Plug the brake booster vacuum hose into its inlet directly behind the throttle body.

Connect the throttle position sensor and electronic throttle control wiring harnesses into their receptacles on the throttle body -- they are different sizes to prevent incorrect connection.

Lower the rearmost part of the windshield cowl so its locator pins slide into the locator holes in the car's body. Press the front of the cowl downward to snap its retaining clips into place. Press the six pin-style cowl retaining clips into place to secure the cowl.

Sit the wiper arms onto the wiper motor output shafts loosely and pivot the arms until the wiper blades align with the lines on the masking tape. Press the arms downward onto the output shafts and torque their retaining nuts to 18 foot-pounds. Lift the wiper blades and remove the tape.

Press the air filter outlet tube onto the outlet on the air filter box and the inlet on the throttle body. Tighten its two hose clamps to 35 inch-pounds. Press the fuel vapor tube and crankcase vent tube into their respective inlets on the air filter outlet tube.

Install the negative battery cable to the negative battery terminal, then tighten its retaining bolt to 62 inch-pounds. Remove the memory saver from the vehicle.

Filling and Bleeding the Cooling System

Pour about half of each gallon of Motorcraft Premium Gold Engine Coolant, or an equivalent coolant meeting specification No. WSS-M97B51, into the two clean 1-gallon sealable containers. This creates four half-full gallons of coolant. Fill the four half-full gallons of coolant the rest of the way with clean water. Tighten the caps onto all of the containers and lightly shake them to mix the water and coolant.

Open the air bleed valve in front of the throttle body, using a flat-head screwdriver. Open the heater air bled valve, which is on the rear driver’s side of the engine compartment, near the master cylinder, using a flat-head screwdriver.

Fill the degas bottle to the top of its filler neck with the coolant and water mixture and wait to allow the coolant level to stabilize. Repeat this step until coolant flows from the air bleed valve, then tighten the air bleed valve. Tighten the cap on the degas bottle.

Start the engine and turn the heater to its highest temperature and fan speed settings. Once coolant flows from the heater air bleed valve, tighten it with a flat-head screwdriver. Let the engine idle for five minutes, remove the cap from the degas bottle and refill the coolant level to the “Cold Fill Max” mark on the degas bottle with your coolant and water mixture each time the level drops .

Open the heater air bleed valve one more time with a flat-head screwdriver to release any additional air, and close it again.

Increase the engine speed to about 1,500 rpm and hold it there until hot air comes from the heater vents. Let the engine speed reduce to an idle and verify that hot air continues coming from the heater vents. If there is no hot air at idle, shut the engine off, let it cool, then restart the process from Step 2.

Set the temperature to 75 degrees Fahrenheit and leave the vehicle idling for about two minutes. Shut the engine off and let the vehicle sit until the engine is cool to the touch. Once cool, remove the degas bottle’s cap and refill the degas bottle to the “Cold Fill Max” mark. The LS’ cooling system requires a total of 2.8 gallons to refill it, but the exact amount your LS requires may vary.

Check the gap on all four new NGK FR5AP-11 or equivalent spark plugs using a spark plug gap tool. The correct gap for the 2006 Impreza is between 0.039 and 0.043 inches. Exchange any incorrectly gapped spark plugs for new ones, as you cannot adjust the gap on these plugs.

Loosen the hose clamp on the engine side of the mass airflow sensor with a flathead screwdriver. Press and hold the unlocking button on the MAF sensor’s wiring harness and unplug the harness from the receptacle. Unclasp the two latches holding the top half of the air cleaner box to the lower half. Lift the top half of the air cleaner box and the MAF sensor from the engine compartment.

Pull the air cleaner element from the air cleaner box. Remove the two bolts securing the bottom half of the air cleaner box to the Impreza’s body using a ratchet and socket. Pull the bottom half of the air cleaner box from the engine compartment.

Trace one spark plug wire toward the side of the engine until you find the thick rubber boot that connects the spark plug wire to the spark plug. Grab the spark plug boot and pull it away from the engine with a twisting motion.

Loosen the spark plug from the engine using a ratchet, 6-inch extension and a spark plug socket. Pull the ratchet, extension and socket from the spark plug tube to remove the spark plug; the spark plug socket has a rubber insert that holds the spark plug inside it to ease removal.

Remove the old spark plug from the spark plug socket and press a new spark plug into the spark plug socket. Thread the new spark plug into the engine using the spark plug socket and 6-inch extension. If you feel any resistance as you thread the new spark plug, immediately remove it and thread it in again.

Inspect the removed spark plug wire for any defects, including excessive aging, brittleness, cracks or breaks. If any defects exist, replace all four spark plug wires.

Apply a small amount of dielectric grease to the inside of the spark plug wire boot. Insert the spark plug wire boot into the spark plug tube and press the boot inward until you feel it click onto the spark plug.

Repeat steps 3 through 8 to replace the other right side spark plug.

Set the lower half of the air cleaner box into the engine compartment, aligning its bolt holes with those in the Impreza’s body. Hand-thread the air cleaner box’s bolts, then torque them to 25 foot-pounds with a torque wrench and socket. Set the air cleaner element back into the lower half of the air cleaner box.

Set the top half of the air cleaner box onto the lower half, guiding the MAF sensor into the air intake tube. Tighten the hose clamp on the air intake tube with a flat-head screwdriver to secure it onto the MAF sensor. Plug the wiring harness into the receptacle on the MAF sensor, then press the clasps over the top half of the air cleaner box until they snap into place.

Left Side Spark Plugs

Loosen the nut on the negative battery cable end’s pinch bolt using a combination wrench. Pull the negative battery cable end upward and off the battery. Lift the rubber cover off the positive battery cable end and loosen the nut on its pinch bolt with a combination wrench. Pull the positive battery cable from the battery.

Remove the two nuts securing the battery tie-down bar using a combination wrench. Lift the battery tie-down bar off the battery, then lift the battery off its tray and out of the engine compartment. Use caution, as batteries are deceptively heavy.

Remove and install the spark plugs by following steps 3 through 9 under “Right Side Spark Plugs.”

Set the battery onto its tray and lower the tie-down bar onto the battery, guiding the tie-down bar’s mounting studs through the holes in the bar. Hand-thread the nuts onto the tie-down bar’s mounting studs, then snug them with a combination wrench.

Reconnect the positive battery cable end to the positive battery terminal, then torque the pinch bolt’s nut to 3 foot-pounds with a torque wrench and socket. Press the negative battery cable end onto the negative battery terminal, then torque its nut to 3 foot-pounds.

Items you will need

4 new NGK FR5AP-11 or equivalent spark plugs

Spark plug gap tool

Flathead screwdriver

Ratchet

Socket set

6-inch extension

Spark plug socket

Torque wrench

New spark plug wires (optional)

Dielectric grease

Combination wrench set

How to Install Spark Plugs on the 2001 Subaru Forester

Check the gap on each of the new plugs using a feeler gauge to be sure each one is correct. The proper gap for the 2001 Subaru Forester is 0.031-inch. Disconnect the battery cables, starting with the negative terminal, by loosening the terminal nuts with a wrench. Remove the battery from the Subaru.

Unplug the mass airflow sensor from the duct on the air filter box. Remove the air intake assembly by removing the three bolts using a socket and ratchet. One is at the front of the intake, one at the left side and one on the right side at the bottom. Loosen the clamp on the air intake duct using a flat-head screwdriver and pull the assembly away from the engine.

Disconnect the wire from the ignition coil using a wrench to loosen the nut if your Subaru has a turbo charger. Remove the bolts securing the windshield washer tank to the Subaru using a wrench and move it aside to gain clearance for the No. 4 spark plug at the right, rear corner of the engine. Do not disconnect the hoses on the tank. Disconnect the wires from the windshield washer motor if your vehicle has a turbo charger. Remove the ignition coil from the automobile using a socket and ratchet if it has a turbocharger.

Grasp the boot of the spark plug wire with your hand and pull the boot off the spark plug. Do not pull by grabbing the plug wire itself or you will damage it. Remove the spark plug from the engine using a spark plug socket, extension and ratchet. You may have to use a universal joint for the socket to gain easier access on the plugs at the back of the engine.

Install the plug and torque it to 15 foot-pounds using the torque wrench. Install the wire on the plug and push firmly until you feel it snap on the plug. Repeat the process with the next plug until you have changed them all.

Put the windshield washer reservoir back in place on the right side and install the retaining bolts using a wrench. Connect the wires to the windshield washer motor if your Subaru has a turbocharger. Install the air intake assembly and tighten the bolts with a socket and ratchet. Tighten the duct clamps using a flat-head screwdriver.

Install the ignition coil using a socket and ratchet to tighten the bolts if your Subaru has turbocharger. Connect the electrical wire to the coil and tighten the nut with a wrench. Place the battery in the car and connect the battery terminals. Tighten the terminal nuts with a wrench.

Items you will need

Feeler gauge

Wrench set

Flat-tip screwdriver

Socket set

Spark plug socket

Socket extension

Socket universal joint

Torque wrench

How to Install Spark Plugs in a Pontiac Firebird

Open the engine compartment and pull the first plug wire off. Remove the spark plug with the spark plug socket, extension and ratchet. Discard the plug.

Open a new spark plug and use the feeler gauge to check the gap. Spark plugs are pre-gapped at the manufacturing facility but you should always check them. The gap should be .50 hundredths. The gap in the spark plug is the space between the electrode and the small bent piece of steel at the top of the plug. The feeler gauge is a tool used to check the gap.

Put the new plug into the engine and tighten snugly with the socket and ratchet. Push the spark plug wire back onto the plug and push it firmly until you feel it snap back into place. Repeat the process for each spark plug until you have replaced them all.

Items you will need

Spark plug socket

Ratchet

Extension

Feeler gauge

How to Install Spark Plugs in a Mercedes Benz

Open the hood. Your Mercedes Benz may have an engine cover. If so, remove it. Begin by locating and removing the coil packs, which usually cover the spark plugs. Use the appropriate ratchet set by checking the vehicle manual if needed, then gently loosen the coil pack. Pull up on the coil pack and turn slightly until it comes completely free from the engine. Disconnect any wires or wire harness if necessary. Notice the spark plug directly underneath.

Loosen the old spark plug using the same ratchet. Use tool extensions and/or spark plug sockets if needed. Grab the spark plug with a free hand and gently pull until it is free from the engine. If the plugs have not been changed for some time, rust or fusion may have occurred, so be cautious of this and do not pull too hard. You want to avoid damage and not leave behind any pieces of the old plug.

Take the new spark plug and gap it using the gapping tool set after checking the automobile manual for exact gap settings. Now, install the newly gapped spark plug into the open spot from where the old plug was removed. Use the ratchet and extensions needed to firmly tighten the new spark plug securely into place. Replace the coil pack and any wiring that was removed.

Repeat these three steps until all spark plugs are replaced. Replace the coil packs and any disconnected wires. Reconnect the battery then start your car to make sure the plugs have been installed correctly.